The Mavuradonha Layered Complex: Neoproterozoic ... - ArchiMeD

4.1.3 Ocellar Gneiss.............................................................................................................. 53
4.2 Mineral chemistry of samples from the Mavuradonha Layered Complex .................. 53
4.2.1 Garnet ..........................................................................................................................54
4.2.2 Pyroxene ...................................................................................................................... 60
4.2.2.1 Clinopyroxene.............................................................................................................. 60
4.2.2.2 Orthopyroxene ............................................................................................................. 62
4.2.2.3 Pigeonite ...................................................................................................................... 62
4.2.3 Plagioclase ................................................................................................................... 63
4.2.4 Amphibole ................................................................................................................... 64
4.2.5 Scapolite ...................................................................................................................... 65
4.3 PT evolution of the Mavuradonha Layered Complex.................................................. 65
4.3.1 Granulite-facies PT conditions .................................................................................... 65
4.3.2 Retrograde PT evolution.............................................................................................. 71
4.3.3 PT conditions calculated using TWQ .......................................................................... 72
4.4 Summary and interpretation of textures and PT-evolution of the Mavuradonha
Layered Complex......................................................................................................... 75
5 Geochemistry ...................................................................................................78
5.1 Classification of the metagabbros................................................................................ 80
5.2 Major and trace element variations.............................................................................. 81
5.2.1 Mavuradonha Layered Complex ................................................................................. 81
5.2.2 Nyamhanda Inlier and Chimwaya Hill Inlier............................................................... 86
5.3 TiO2, LIL and HFS element correlations..................................................................... 90
5.4 Summary and interpretation......................................................................................... 90
5.4.1 Mavuradonha Layered Complex ................................................................................. 90
5.4.2 Nyamhanda Inlier and Chimwaya Hill Inlier............................................................... 93
6 Geochronology and zircon-cathodoluminescence ........................................97
6.1 Cathodoluminescence imaging .................................................................................... 97
6.2 Zircon U-Pb and Pb-Pb geochronology....................................................................... 99
6.2.1 Mavuradonha Layered Complex ................................................................................. 99
6.2.1.1 Metagabbro sample ZZB 123 ...................................................................................... 99
6.2.1.2 Ferro-metagabbro sample ZZB 166........................................................................... 106
6.2.1.3 Summary of age interpretation for zircons from the Mavuradonha Layered
Complex..................................................................................................................... 107
6.2.2 Pegmatites within the Mavuradonha Layered Complex............................................ 109
6.2.2.1 ZZB 60: pegmatite, northern Mavuradonha Mountains ............................................ 109
6.2.2.2 ZZB 128: pegmatite, south of the Mavuradonha Mts................................................ 109
6.2.2.3 Interpretation.............................................................................................................. 112
6.2.3 Ocellar Gneiss............................................................................................................ 112
6.2.3.1 ZIM 30 (Fig. 6-9 a & b; Fig. 6-10 a) ......................................................................... 112
6.2.3.2 ZIM 56 (Fig. 6-9 c & d; Fig. 6-10 b) ......................................................................... 113
6.2.3.3 ZIM 55 (Fig. 6-9 e & f; Fig. 6-10 c) .......................................................................... 116